Picosecond pulsed laser microstructuring of metals for microfluidics

Micromachining with short and ultra-short laser pulses has evolved over the past years as a versatile tool that can be employed for the creation of microstructured surfaces. A microstructured surface modifies the way a fluid interacts with a solid surface. Surface microstructuring can then be employed to provide surfaces with certain functionalities. By proper adjustment of the laser machining conditions, well defined surface topographies can be created with sufficient accuracy. This allows to investigate the fluid/microstructured surface interactions. However, the relation between the applied laser parameters and the shape of the emerging microstructure has not been systematically studied in literature. This thesis is dedicated to the study of some of the mechanisms underlying different fluid/microstructured surface interactions. First, an empirical model is developed for the prediction of the surface topography emerging from a process driven by short laser pulses. To this end, average ablated profiles are measured and employed for the simulation of the laser microstructuring pro- cess. The accuracy of the model is assessed by establishing a direct comparison between simulated and measured surface profiles. The model is shown to accurately reproduce the surface topography obtained from a laser micromachining process, within a certain processing window. Next, the developed model is employed as a tool for the design of fluidic microstructures, as well as for the investigation of different fluidic functionalities, based on the generated microstructures. Moreover, simplified models are introduced, to relate the geometry of a microstructure to the fluid-microstructure interaction. This allows the calculation of the laser processing parameters that are required to obtain a desired functional microstructured surface. Further- more, modifying key geometrical parameters, for example depths or slopes of the microstructure, allows investigating some of the fluidic mechanisms responsible for the functionality. Hence, additional knowledge on the fluid/microstructured surface interaction is gained by this approach.